Medical devices often require accurate weight sensors to measure the weight of fluid collection bags being used to collect filtrate from ultrafiltration, continuous renal replacement therapy (CRRT) and other such medical therapies. Generally, weight sensors having high repeatability and accuracy tend to be fragile and susceptible to damage. In contrast, structurally robust weight sensors that can withstand impacts and unexpected high forces tend to be less sensitive and prone to inaccuracies in their weight measurements. In appears that the opposing requirements of weight sensor robustness and weigh measurement accuracy often require that sacrifices be made by the designer to the robustness and accuracy of the weight sensor under design. Nevertheless, there is a long-felt need for a weight sensor for medical devices and particularly for weighing medical fluid collection bags that is structurally robust and yield accurate, sensitive and repeatable weight measurements.
Accurate weight sensors are particularly necessary when weight measurements are applied to trigger alarms in a medical device. These alarms are often triggered by weights that are subject to narrow tolerances and the alarms are established to protect patient safety. Further, medical devices with narrow tolerances in weights that trigger an alarm are prone to have high incidences of alarms, many of which are triggered by non-dangerous events. A weight sensitive alarm may be triggered as a medical device is intentionally moved. Movement of a medical device may not suggest a dangerous condition, and should not trigger an alarm. An alarm may need to be triggered if there is a rapid change in the weight of a fluid collection bag, which may indicate a dangerous condition. A nurse or other medical practitioner may become numb to alarms from a medical device, if alarms are frequently triggered by benign events. For example, frequent alarms triggered by intentional movement of a medical device movement may result in nurses not responding promptly to any alarm from that device including those alarms caused by rapid changes in bag weight. The failure to promptly respond to an alarm triggered by a dangerous condition may put the patient in danger. Thus, there is a great need to make alarms more robust to false alarms while ensuring that alarms be reliably triggered by excessive weight gain in a fluid collection bag.